Currently, the most widely used catalyst for olefin polymerization is a magnesium chloride-supported Zeigler-Natta catalyst. The magnesium chloride-supported Zeigler-Natta catalyst is a solid catalyst component generally comprised of magnesium, titanium, halogen and an electron-donating organic compound. When it is used in polymerization of alpha-olefins such as propylene, it can be used together with an organic aluminum compound as a co-catalyst and an organic silane as a stereoregularity control agent at an appropriate mixing ratio. Since such supported type solid catalysts for olefin polymerization are applied to various commercial processes such as slurry polymerization, bulk polymerization, gas phase polymerization and the like, they need to meet the requirements regarding particle morphology including an appropriate particle size, uniformity in particle distribution, minimized amount of fine particles, high bulk density and the like, as well as basic requirements including high catalyst activity and stereoregularity.
As a method for improving the particle morphology of a support for olefin polymerization catalysts, those using recrystallization and reprecipitation, spray drying, and chemical reactions have been currently known in the art Among them, one of the methods using chemical reactions, which uses dialkoxy magnesium as a support for catalyst preparation, obtained by reacting magnesium with an alcohol, has been attracting more attention, since the method provides a catalyst having much higher activity than those obtained from other methods, and polymers having high stereoregularity.
When using dialkoxy magnesium as a support, the particle shape, particle size distribution, bulk density and the like of the dialkoxy magnesium directly affect the catalyst and the particle properties of the resulted polymers. Therefore, it is demanded to develop a highly uniform and spherical dialkoxy magnesium support having sufficiently high bulk density through the reaction between magnesium and an alcohol.
Various methods for preparing dialkoxy magnesium having a uniform shape have been disclosed in literatures from prior arts. U.S. Pat. Nos. 5,162,277 and 5,955,396 suggest a method for preparing a support having a size of 51-10 μm, by carboxylating amorphous diethoxy magnesium with carbon dioxide to produce magnesium ethyl carbonate and recrystallizing the magnesium ethyl carbonate in a solution with various additives and a solvent. Further, Japanese laid-open patent application No. Heisei 06-87773 discloses a method for producing spherical particles by spray-drying an alcoholic solution of diethoxy magnesium carboxylated with CO2, and decarboxylating the resulted product. However, such conventional methods requires complex processes involving many kinds of raw materials, and can provide neither agreeable particle size nor shape of the resulted support.
In Japanese laid-open patent application Nos. Heisei 03-74341, Heisei 04-368391 and Heisei 08-73388, provided are methods for preparing diethoxy magnesium in spherical or elliptical shape by reacting metal magnesium with ethanol in the presence of iodine However, since said method involves an extremely rapid reaction which generates great reaction heat together with lots of hydrogen during the reaction process, it is difficult to adjust the reaction rate to the desired level. Further, there is another problem that the resulted diethoxy magnesium support comprises lots of fine particles or mass particles having different shape which are resulted from agglomeration of several particles. Therefore, if a catalyst prepared from such support is used, as it is, for olefin polymerization, it would cause problems such that the particle size of the resulted polymer become excessively large, or an operational failure would occur owing to the collapse of particle shapes by polymerization heat during the polymerization process.
The mainly used initiators for the above said preparation of dialkoxy magnesium support, include for example iodine which is a halogen; dibromoethane which is an organic halogen compound; and magnesium chloride, magnesium bromide and magnesium iodide which are metal halogen compounds.
The halogenated nitrogen compound, which has been used as an initiator for the first time by the present invention, has been reported in Tetrahedron vol. 59, p. 6739; Catalysis Communications vol. 7 p. 399; Tetrahedron Letters vol. 46, p. 5293 for its use in alcohol oxidation, acylation, alcohol protecting reaction, halogenation and the like. However, its use in the preparation of dialkoxy magnesium support has not been reported yet.